Improvement in the chlorine evolution activity of an SnOx@IrO2–Ta2O5 electrode and its application in the electrolysis of an extremely dilute chlorine-containing solution†

Abstract

It is imperative to solve the problem of the electrolytic efficiency of chlorine evolution in extremely dilute chlorine-containing solutions for electrochemical advanced oxidation processes, electrochemical antifouling and chlorine-containing disinfectant preparation. In this paper, an IrO₂–Ta₂O₅ electrode is modified using SnO_x, and the activity and selectivity of the chlorine evolution reaction (CER) are successfully improved. The modification of SnO_x changes the electronic structure of IrO₂–Ta₂O₅, thus affecting the electrochemical reaction process and mechanism. Compared with the CER activity of the IrO₂–Ta₂O₅ electrode, the CER activity of the SnO_x@IrO₂–Ta₂O₅ electrode is increased, whereas the OER activity is decreased. At a current density of 50 mA cm⁻², the potential difference between the CER and OER of the SnO_x@IrO₂–Ta₂O₅-3 electrode is 254 mV, which is 89 mV higher than that of the IrO₂–Ta₂O₅ electrode. This proves that the selectivity of the CER at the SnO_x@IrO₂–Ta₂O₅ electrode has been improved. Due to the low concentration of chloride ions, the current efficiency of the IrO₂–Ta₂O₅ electrode is only 10.7%. The current efficiency of the SnO_x@IrO₂–Ta₂O₅-1(2,3) electrode increases to 23.6%, 36.7% and 49.6%, respectively. For the IrO₂–Ta₂O₅ electrode, its rate-determining step (RDS) is the second electron transfer. However, for the SnO_x@IrO₂–Ta₂O₅-3 electrode, its RDS is electrochemical desorption. It can be inferred that the modification of SnO_x can accelerate the electrochemical desorption of adsorbed Cl. In addition, the application of the SnO_x@IrO₂–Ta₂O₅ electrode in the preparation of AEW is investigated. The HClO content in AEW2 (prepared using the SnO_x@IrO₂–Ta₂O₅-3 electrode) is 1.85 mmol L⁻¹, which is 4.6 times of that in AEW1 (prepared using the IrO₂–Ta₂O₅ electrode).